The catalytic hydrogenation of aromatics is well known. DE 4 310 971 discloses a Ni—Al2O3 catalyst comprising contents of Ni (Nickel) from 10 to 60 weight-% for the hydrogenation of aromatic hydrocarbons. The Ni crystallites have an average diameter of 15 to 50 nm. Furthermore, the catalyst employed is characterised in that 15 to 75% of the pore volume is allotted to pores having a diameter of >100 nm. The large Ni crystallites indicate that the hydrating metal is used inadequately.
EP 0 290 100 relates to formed Ni-theta-Al2O3 catalysts comprising 5 to 40 weight-% of Ni for hydrogenation of hydrocarbons which contain aromatics. The catalyst support employed includes virtually no pores smaller than 2.0 nm. The Ni dispersion of the catalysts employed is very high. The surface area of Ni ranges from 80 to 300 m2/g Ni. When used with feeds having a slightly higher content of sulphur these catalysts age very quickly, leading to a deterioration of their performance.
EP 0 398 446 discloses a catalyst system for hydrogenation of aromatics in solvents and white oil having high resistance against sulphur compounds. On a support the catalysts separately contain a hydrogenating component and a metal oxide. As metals Cu, Ni, Pt, Pd, Rh, Ru, Co and mixtures thereof and as a metal oxide component the oxides of Ag, La, Sb, V, Ni, Bi, Cd, Pb, Sn, V, Ca, Sr, Ba, Co, Cu, W, Zn, Mo, Mn, Fe and mixtures thereof are exemplified. According to this disclosure the catalyst may consist of Al2O3, SiO2, Al2O3.SiO2, TiO2, ZrO2 and MgO.
According to EP 0 974 637 even higher resistance against sulphur is achieved by a combination of a supported catalyst comprising noble metal, a catalyst comprising metal oxide and a Ni—SiO2 catalyst. Thus, a supported Pt/Pd-catalyst is for example positioned at the reactor head and a mixture of ZnO extrudates and Ni—SiO2 extrudates is placed below.
EP 1 262 234 discloses catalysts for the hydrogenation of aromatics comprising 0.1 to 2.0 weight-% of a group VIII noble metal on SiO2—MgO support having a MgO content of 25 to 50 weight-% which show a low tendency to crack.
Those prior art catalysts comprising noble metal have the disadvantage that they are expensive. On the other hand, prior art Ni—Al2O3 catalysts, which are cheaper, are typically less effective and suffer from very high sensitivity to sulphur and chlorine compounds.
It is an object of the invention to provide a catalyst and a process for the hydrogenation of aromatics and other unsaturated organic compounds which overcomes at least one drawback associated with the prior art. Specifically, a technical problem underlying the present invention is to provide a catalyst and a process for the hydrogenation of aromatics and other unsaturated organic compounds which is particularly effective.
The present invention provides nickel (Ni)-catalysts which are highly effective and active in the hydrogenation of aromatics and other unsaturated organic compounds. Advantageously, the catalysts of the invention are also particularly poison resistant.
On the one hand, the invention is based on the appreciation that dispersion of Ni in a Ni-catalyst in a “semi-eggshell distribution”, as further defined herein, contributes greatly to effectiveness of the catalyst in hydrogenation.
The term “semi-eggshell distribution” as used herein refers to a concentration distribution whereby the concentration in an outer shell region of the catalyst is higher than in a remaining centre of the catalyst, in particular as detailed below.
Thus, according to a first aspect, the invention resides broadly in a Ni catalyst comprising a support and Ni wherein a centre of the catalyst comprises a base Ni concentration and a remaining outer shell region of the catalyst comprises an increased Ni concentration.
The invention is also based on the appreciation that a multimodal, specifically bimodal, particle size distribution of Ni crystallites, as further defined herein, contributes significantly to the effectiveness of Ni catalysts in hydrogenation.
Therefore, according to a second aspect, the invention resides broadly in a Ni catalyst comprising a support and Ni, wherein the size distribution of Ni crystallites of the catalyst is bimodal, with a first proportion of the Ni crystallites having an average size (diameter) of 1.0 to 2.5 nm and a second, remaining proportion of the Ni crystallites having an average size (diameter) of 3.0 to 4.5 nm.
A particular synergy has been observed by the inventors in Ni catalysts between semi-eggshell Ni distributions and bimodal Ni crystallite size distributions, as defined herein. In particular, without wishing to be bound by theory, it is thought that in those catalysts of the invention which exhibit both a semi-eggshell distribution of Ni and a bimodal Ni crystallite size distribution, larger Ni crystallites are particularly prominent in the outer shell region of the catalyst (i.e. more prominent than in the centre), thereby helping to shield smaller and more active Ni crystallites in the centre of the catalyst from catalyst poisons.
Thus, according to a third aspect, the invention resides broadly in a Ni catalyst comprising a support and Ni, wherein Ni is dispersed in a semi-eggshell distribution as defined anywhere herein, and wherein the size distribution of the Ni crystallites of the catalyst is bimodal as defined anywhere herein.
For example, the invention provides a particularly effective solution to the underlying technical problem by residing, according to a fourth aspect, in a Ni-catalyst, comprising a support and Ni, wherein the size distribution of the Ni crystallites is bimodal with 30 to 70% of the Ni crystallites having an average size of 1.0 to 2.5 nm and the remaining Ni crystallites having an average size of 3.0 to 4.5 nm, and wherein the Ni is distributed in an outer shell region of the catalyst having a penetration depth of 3 to 15% of the catalyst diameter and the centre of the catalyst in a concentration ratio in the range of from 3.0:1 to 1.3:1 (outer shell:centre) which hereinafter is abbreviated as 3.0 to 1.3.
In the context of the present invention, the diameter of a catalyst (i.e. catalyst particle) is the longest internal straight length of said catalyst passing through the geometric middle of the catalyst. The geometric middle lies in the catalyst centre and is the point, or plurality of points, having the greatest minimum distance from the catalyst surface. The geometric middle may correspond to the centre of gravity of the catalyst, provided that it falls within the catalyst.
The term “penetration depth” is used herein as a parameter for defining the thickness of the outer shell region, and consequently also the dimensions of the catalyst centre, which makes up the remainder of the catalyst. The penetration depth defines the cross-sectional depth of the outer shell region and therefore equals the distance between the surface of the catalyst and the circumference of the catalyst centre.
The penetration depth may be an assigned depth value, taken for example to be a defined percentage of the catalyst diameter, or an absolute distance. The assigned depth value may be set as any number falling within any of the penetration depth ranges (relative or absolute) disclosed herein. Alternatively, the penetration depth may be defined by a range of assigned depth values.
The penetration depth may correspond to an actual penetration depth value. The actual penetration depth value of the catalyst is defined as the minimum cross-sectional depth (measured from the catalyst surface in increments of 5 μm in the direction of the nearest point of the geometric middle of the catalyst) at which the Ni concentration lies within plus or minus (±) 10% of the Ni concentration at the geometric middle of the catalyst. Where the geometric middle comprises a plurality of points, the Ni concentration at the geometric middle is taken as an average (measured at 5 μm intervals if the points are continuous). The Ni concentration at the geometric middle is determined in weight-% and rounded up to the nearest weight-%.
Thus, aspects of the present invention envisage a very specific Ni-distribution provided over substantially the entire cross-section of a catalyst (or catalyst particle) in a semi-eggshell distribution such that the Ni is distributed in an outer shell region and the centre of the catalyst in a range of concentration ratios of from 3:1 to 1.3:1, which equals a range of concentrations from 3.0 to 1.3, each ratio calculated as Ni concentration in the outer shell region of the catalyst having a penetration depth of 3 to 15% of the catalyst diameter to the Ni concentration in the centre of the catalyst.
Surprisingly, it has been found that the catalysts of the present invention, which typically do not exhibit the large surface areas disclosed in EP 0 290 100, still have high performance. This is particularly noted where the invention foresees a semi-eggshell distribution of the Ni in the catalyst in combination with a particular size distribution of Ni crystallites. Furthermore, the catalysts of the present invention have the advantage that production costs are low. The catalysts of the present invention also provide advantageous resistance against contamination with sulphur and chlorine compounds.
Advantageously, the ratio of the Ni concentration in the outer shell region to the Ni concentration in the centre of the catalysts according to the invention may be in a range from 3.0:1 to 1.3:1, preferably 3.0:1 to 1.5:1, more preferably 2.8:1 to 1.4:1 or 2.5:1 to 1.5:1, and in particular 2.5:1 to 1.3:1 (each outer shell:centre).
The Ni concentration in the outer shell region and the centre of the catalyst is determined in weight-%.
The Ni concentration in the outer shell region is conveniently determined by measuring at 5 μm intervals, from the surface of the catalyst towards the nearest point of the geometric middle of the catalyst, and taking an average of the resultant Ni concentration readings. The concentration in the outer shell region is rounded to the nearest weight-%.
The Ni concentration in the centre of the catalysts of the invention may typically be homogenous or substantially homogenous (i.e. vary by less than ±10%). Where variations in Ni concentration occur, an average of measurements at 5 μm intervals is taken as the concentration in the centre. The concentration in the catalyst centre is rounded to the nearest weight-%.
The outer shell region of the catalysts according to the invention may advantageously be characterized by a maximum penetration depth of up to 15%, 13%, 10%, 8% or 7% of the catalyst diameter. A minimum penetration depth may be 3%, 5%, or 7% of the catalyst diameter. Specifically, the penetration depth may lie in the range of from 3 to 15% of the catalyst diameter, preferably in the range of from 3 to 10%, more preferably in the range of from 3 to 8%, and in particular in the range of from 3 to 7%, of the catalyst diameter.
A single cross-section may be taken as representative in defining the catalysts of the invention. Thus, the invention encompasses any catalyst having at least one cross section that conforms to the definitions (e.g. relating to penetration depth, outer shell and centre) provided herein. Preferably all cross sections of the catalysts may fall within the definitions provided herein.
Advantageously, the average size (diameter) of the Ni crystallites of the catalysts of the invention may be from 1.0 to 4.0 nm, preferably from 1.5 to 3.5 nm, more preferably 1.6 to 2.4. In preferred embodiments of the present invention, the size (diameter) distribution of the Ni crystallites may be bimodal. In particularly preferred embodiments, the present invention foresees a bimodal size distribution, wherein 30 to 70%, preferably 40 to 60%, more preferably 45 to 55% of the particles have an average size of 1.0 to 2.5, preferably 1.2 to 2.2, more preferably 1.4 to 2.0, in particular 1.6 nm and the remaining percentage of the particles adding up to 100% have a different average size, in particular 70 to 30% of the particles, preferably 60 to 40%, more preferably 55 to 45% of the particles have an average size of 3.0 to 4.5, preferably 3.2 to 4.2, more preferably 3.4 to 4.0.
In further preferred embodiments of the present invention, the pore volume of the catalysts may be 0.2 to 0.7 ml/g, preferably 0.3 to 0.6 ml/g, more preferably 0.4 to 0.5 ml/g.
Advantageously, the portion of the pore volume having pore radii of >5.0 nm may be 75 to 100%, preferably 75 to 90%, more preferably 75 to 80%, in particular at least 75.5%, preferably 75.5 to 100% or 75.5 to 90%.
In further preferred embodiments of the present invention, the Ni content in the catalysts may be 5 to 70 weight-%, preferably 10 to 60 weight-%, and most preferably 10 to 35 weight-%. A minimum Ni content of 18 weight-% is also preferred.
Preferably, the Ni content in the catalysts may be 10 to 24 weight-%. In particular, the Ni content in the catalysts may be 10 to 24 weight-% and the concentration ratio of Ni of the outer shell region of the catalysts to the Ni of the centre of the catalysts may be in a range from 2.5 (2.5:1) to 1.3 (1.3:1).
Alternatively, the Ni content in the catalysts may advantageously be 24.1 to 35 weight-%. In particular, the Ni content in the catalyst may be 24.1 to 35 weight-% and the concentration ratio of the Ni of the outer shell region to the Ni of the centre of the catalyst may be in a range from 3.0 (3.0:1) to 1.5 (1.5:1).
The term “weight-%” as used herein refers, if not otherwise stated, to the percentage weight relative to the weight of the dry catalyst, and “weight-%” values are based on elemental form unless specified otherwise. In the context of the present invention, the components of the catalysts are to be selected in an overall amount to add up to 100 weight-%, most preferably not to exceed 100 weight-%.
In further preferred embodiments of the present invention, the specific Ni surface area of the catalysts may be ≦150 m2/g Ni, in particular 10 to 140 m2/g Ni, preferably ≦135 m2/g Ni, preferably 80 to 135 m2/g Ni.
In preferred embodiments of the present invention, the support of the catalyst may comprise, preferably essentially consist of, particularly consist of, Al2O3, Al2O3.SiO2 or a mixture of Al2O3 and Al2O3.SiO2. The Al2O3 may preferably comprise gamma and/or theta alumina.
In further preferred embodiments of the present invention, the support of the catalyst may comprise Al2O3 having surface areas (BET surface areas) of 100 to 220 m2/g, preferably of 120 to 220 m2/g, more preferably of 140 to 220 m2/g, in particular preferably of 160 to 220 m2/g. In further preferred embodiments of the present invention, the support may comprise Al2O3.SiO2 having surface areas of 120 to 200 m2/g, preferably of 140 to 200 m2/g, more preferably of 160 to 200 m2/g.
In further preferred embodiments of the present invention, the SiO2 content of the support, in particular the Al2O3.SiO2 support, may be 2 to 8 weight-%, preferably 2 to 4 weight-%, the support adding up to 100 weight-% with Al2O3.
The Ni catalysts of the present invention contain Ni in either its elemental or combined form, preferably in its elemental form.
Advantageously, the catalysts of the present invention may be free of noble metals. In preferred embodiments the catalysts of the present invention are free of metals from the group I, VIII or both of the periodic table of the chemical elements. Preferably, Ni may be the only hydrogenation-active metal present in the catalyst.
In further preferred embodiments of the present invention, the catalysts or catalyst particles may be shaped, for example in the form symmetrical or asymmetrical extrudates, tablets, rings or spheres. Further suitable forms are cylindrical particles, which may be hollow or not, as well as polylobed particles, preferably with 2, 3 or 4 lobes. Preferably, the catalyst may have a diameter from 0.5 to 20 mm, preferably 1 to 15 mm, 1 to 10 mm, 1 to 5 mm, 1 to 3 mm.